Model block-graft copolymer via anionic living polymerization: Preparation and characterization of [poly((4-vinylphenyl)dimethylvinylsilane)-graft-polyisoprene]-block-polystyrene

A model graft copolymer that has well-defined length, number, and position of grafts was prepared via anionic living polymerization. (4-Vinylphenyl)dimethylvinylsilane (VS) was anionically polymerized by cumylcesium in THF at -78 degrees C for 20 min under a pressure of 10(-5) mmHg, and subsequent addition of styrene (St) yielded a PVS-b-PSt block copolymer that could be used as a backbone molecule. PVS has a silylvinyl group on the side chain that converts chemical links between backbone and grafts. Isoprene (Is) was anionically polymerized to yield living polyisoprene, and the resultant PIs(-)Cs(+) and PIs(-)Li(+) solutions were added to THF and benzene solutions of PVS-b-PSt, respectively. After 24 h, backbone coupling was terminated to yield [poly(4-vinylphenyl)dimethylvinylsilane-graft-polyisoprene]-block-polystyrene. The three graft copolymers were prepared. Molecular characterization was carried out by GPC measurement, osmometry, and sedimentation pattern. The M(n) and M(w)/M(n) values of the backbone, grafts, and graft copolymers were determined. The number of grafts per backbone molecule was found to be 10.(0), 10.(9), and 12.(5) for the three graft copolymers, and the position of the grafts was set to the end of the backbone molecule. Spacing and its distribution of the graft points on a backbone molecule were also discussed. Three benzene-cast films formed clear microphase-separated structures, such as spherical and lamellar structures. The composition dependence on the morphology of the graft copolymers was found to differ from that of common block copolymers. These results suggest that the apparent volume fraction of grafts is much larger than the real volume fraction, because the grafts became crowded in the vicinity of the backbone molecule.